Haven't seen an ingenic SoC in a while. One of the few MIPS processors left in the market, everything else is ARM...Have done a bit of work on their older stuff (JZ4755 SoC), good documentation, shame the company got bought out.

I downloaded the rar file, unpacked and took a cursory look at the bin file.

Looks like its possibly encrypted or compressed post header, as I don't see many FF's or 00 strings in the file after the initial header.strings also doesn't show any readable text, which ties in with it being compressed or encrypted.

Really depends on the board you have, and what gpio's are available to use, and how much flash / ram (for user space software etc).

Do you have the Hi3518e SoC SDK?

You'll need the SDK to get started, and compile a rom with kernel, userfs etcMaybe the supplier will give you a ready to use kernel/rom/userfs that you can start from.

You'll need to have a uBoot on the board. Hopefully will have one already, otherwise you'll also need an SPI flash programmer to program the uBoot.You'll need to be able to setup a crosscompiler environment (suggest use Docker or similar virtualized system to setup, then you can migrate easily).You'll need to unpack the SDK, then be able to compile kernel.You'll need to learn how to setup rom in flash.

Suggest read the uCLinux posts from 2011 where I talk about similar things. Its relevant, although not 100% relevant to your particular board.

For your OV file, you'll need to look at the header, and see if its a standard format, or its a custom format.Its more likely to be a custom format. Typically those will have a header with where bits are in the file, and filesize, and maybe crc's.If you're really unlucky, its also sha1 or similar encryption on the file data.